1. Field of the Invention
The present invention is in the field of engineering that deals with the flow of particulate materials and specifically relates to an apparatus for converting a fluctuating input flow into an output flow that is more uniform.
2. The Nature of the Problem
Many types of processing equipment for use with particulate materials--such as continuous screeners, grinders, pugmills, hammermills, blenders, crushers, mixers, and chemical reactors--work at improved efficiency if the flow of particulate material into them is at a constant rate rather than varying or pulsating. These processors are usually fed by a conveyor or feeder--such as a belt, screw, dragchain or flight conveyor. All of these feeders tend to discharge in pulses, as is particularly apparent when the material is supplied by a moving chain of buckets. The present invention interposes between the feeder and the fed processing equipment means for smoothing out the pulses and variations to provide a more uniform feed to the processing equipment, thereby improving its efficiency.
As used herein, the terms "chute" and "hopper" refer to the same apparatus; the distinction lies in how the apparatus is operated. As used herein, both converge downwardly.
When the apparatus is used as a converging chute, the incoming particles simply freefall or tumble through the apparatus, their lateral dispersion being limited by the walls of the apparatus. A pulsed input results in a pulsed output.
In contrast, in a partly full converging hopper, the discharge rate is determined by the slope of the walls and the size of the outlet, and therefore remains approximately constant regardless of how much material is in the hopper, and regardless of variations in the input stream.
Because the efficiency of the processing equipment is greatest when the incoming flow is at a constant rate, operation as a converging hopper is preferable to operation as a converging chute. However, operation as a hopper will not occur unless the mass of particles has accumulated to a minimum height above the outlet, so that the outlet cross section will always be filled with the particulate material. Unfortunately, the minimum height is not likely to be attained in an unaided hopper because the flow rate capacity of a chute is much greater--perhaps by a factor of 10--than the flow rate for operation as a hopper.
In a realistic situation, the chute/hopper apparatus is initially empty, and thereafter an irregular flow of input particles begins. A major problem addressed by the present invention is how to initially accumulate enough material in the chute/hopper apparatus so that operation as a hopper will be initiated.
Over an extended period of time the input must equal the output; otherwise, the hopper will eventually overflow or alternatively become empty. Once established, operation as a hopper is self-sustaining provided the average input flow rate equals the average output flow rate, assuming the variations in the input stream are not too extreme.
In practice neither the input flow rate nor the output flow rate is measured or sensed, and the present invention does not require such measurements. As will be explained in detail below, the present invention solves the problem of maintaining approximate equality between the average input flow rate and the average output flow rate.